Answer: 35*10^3 N/m
Explanation: In order to explain this problem we know that the potential energy for spring is given by:
Up=1/2*k*x^2 where k is the spring constant and x is the streching or compresion position from the equilibrium point for the spring.
We also know that with additional streching of 2 cm of teh spring, the potential energy is 18J. Then it applied another additional streching of 2 cm and the energy is 25J.
Then the difference of energy for both cases is 7 J so:
ΔUp= 1/2*k* (0.02)^2 then
k=2*7/(0.02)^2=35000 N/m
Answer:
The coefficient of kinetic friction 
Explanation:
From the question we are told that
The length of the lane is 
The speed of the truck is 
Generally from the work-energy theorem we have that

Here N is the normal force acting on the truck which is mathematically represented as
is the change in kinetic energy which is mathematically represented as
=>
=>

=> 
=> 
Answer:
560 N/m
Explanation:
F = kx
75 N = k (0.61 m − L)
210 N = k (0.85 m − L)
Divide the equations:
2.8 = (0.85 − L) / (0.61 − L)
2.8 (0.61 − L) = 0.85 − L
1.708 − 2.8L = 0.85 − L
0.858 = 1.8L
L = 0.477
Plug into either equation and find k.
75 = k (0.61 − 0.477)
k = 562.5
Rounded to two significant figures, k = 560 N/m.